Field of Invention
The present invention relates to a steel production technology, and more particularly to a method for preparing low-cost clean steel, which belongs to a field of metallurgical technology
Description of Related Arts
Cleanliness is an important sign reflecting overall quality of steel. The cleanliness is usually judged from content of harmful elements in the steel, and number, shape as well as size of non-metallic inclusions. “Clean and pure” steel is typically obtained by reducing and controlling residual elements such as P, S, N, H, T.O, C, Al, and Ti in the steel. The elements affect steel performance in a single or combined form. In order to improve the intrinsic quality and performance of the steel, basic requirements for iron and steel metallurgy technology development are: (1) maximizing removal of harmful elements such as S, P, N, H, and T.O (wherein sometimes C is comprised) in steel; (2) precisely controlling element contents in steel; (3) strictly controlling inclusion quantity, composition, morphology, size and distribution, and converting the inclusion to harmless or even beneficial elements; and (4) casting without defect. With development and application of clean steel metallurgy technology, requirements for ferroalloy and auxiliary materials for steelmaking are stricter. For example, in order to meet the increasing toughness requirements for pipeline steel, especially the increasing requirement for HIC-resistance performance of acidic gas pipeline, the content of S in the steel keeps decreasing. For auto sheet (or car shell), C, N, and T.O should be less than 20 ppm. Diameter of inclusion in tire radial should be less than 10 μm. In order to improve the anti-contact fatigue performance, T.O in ball bearing steel should be less than 10 ppm, or even lower. With the rapid development of steel metallurgy technology for improving the cleanliness, T.O+N+P+S+H in the steel has been equal to or less than 80 ppm during production. CN1480549, published Mar. 10, 2004, discloses a barium-contained clean steel and a production method thereof, which relates to a field of alloy steel, and particularly to barium-contained alloy steel. The production method of the barium-contained clean steel comprises steps of: after melted in a conventional electric furnace, converter, or other vacuum melting furnace, refining in a refining apparatus, and barium-alloying at a late stage of refining; before adding a barium alloying element, adding aluminum deoxidizer or silica-aluminum for pre-deoxidizing, then blowing argon, and adding barium alloy for producing the barium-contained clean steel. However, the cleanliness of the final product is not sufficient, and the published element percentages by weight in the clean steel are: Ba 0.0001˜0.04%, S≦0.035%, P≦0.035%, A, B, C and D type inclusions are generally of 1.0˜0.5 degree, which do not meet the requirements of a higher cleanliness.
In addition, clean steel standard is not only a technical problem. First of all, it is an economic problem. For producers to improve the cleanliness of steel with their own equipments and technology, unless the required cleanliness is too high, the cleanliness object is usually able to be achieved. As a result, the production cost is bound to increase, and the user has to pay for the desired high cleanliness.